It is known in the field of optical communications to use optical wavelengths as optical carriers for carrying digital or analog information. Also, the different wavelengths may be used to discriminate one set or channel of information from another. When a plurality of wavelengths are coupled or multiplexed onto a single fiber, this is called wavelength division multiplexing (WDM). Use of such WDM increases the overall bandwidth of the system.
There is a need in such systems to switch packets of optical information passing along one fiber to any of a number of other fibers, according to the wavelength of the optical signal. Such a switch is known as an optical router or a wavelength selective switch. A number of wavelength dependent switches and routers exist in the prior art. In co-pending PCT Applications. PCT/IL2002/00511, PCT/IL2003/01002 and PCT/IL2006/00590, all hereby incorporated by reference, each in its entirety, there are disclosed wavelength selective switches wherein an input optical signal is spatially wavelength-dispersed and polarization-split in two preferably perpendicular planes. The wavelength dispersion is preferably performed by a diffraction grating, and the polarization-splitting by a polarized beam splitter. A polarization rotation device, such as a liquid crystal polarization modulator, pixelated along the wavelength dispersive direction such that each pixel operates on a separate wavelength channel, is operative to rotate the polarization of the light signal passing through each pixel, according to the control voltage applied to the pixel. The polarization modulated signals are then wavelength-recombined and polarization-recombined by means of similar dispersion and polarization combining components as were used to respectively disperse and split the input signals. At the output polarization recombiner, the direction in which the resulting output signal is directed is determined by whether the polarization of the particular wavelength channel was rotated by the polarization modulator pixel, or not. PCT Application Nos. PCT/IL2003/01002 and PCT/IL2006/00590 also incorporate lateral expansion of the polarized beams in the plane of the dispersion.
Such fast, wavelength selective, optical switch structures are capable of use in WDM switching applications, but are generally limited to 2×2 configurations, for use as channel blockers or attenuators. In U.S. Pat. No. 7,092,599 to S. J. Frisken for “Wavelength Manipulation System and Method”, there is described a wavelength manipulation system using an LCOS phased array, with an optical arrangement including a spherical mirror and a cylindrical lens for maintaining collimation of the input beams in the direction of dispersion, and for focusing of the input beams in the direction perpendicular to the direction of dispersion. In published U.S. Patent Application No. 2006/0067611 for “Wavelength Selective Reconfigurable Optical Cross Connect”, there is described an optical coupling device using an LCOS phased array, with an optical arrangement including at least a cylindrical mirror and a cylindrical lens.
There therefore exists a need for a new optical, multi-pole, multi-way wavelength selective switch structure having a simple optical structure, for use in channel routing applications, with the addition of add and drop functionalities.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.